stroker engine balancing

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abdywgn

abdywgn

dismantler
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Looking to do a forged crank,internal balance engine.SFI balancer and 10.5" steel flywheel(these parts are neutral balance).Rods would be H beams in std. length.What weight piston would be needed to keep it internally balanced w/o adding weights to the crank?Would each manufactor be different(Eagle,Ohio Crank,Scat...?).Thanks,Bob
 
Lighter pistons/rods ect. are better but the real factor is the crank.A forged crank is dense and has enough weight to internal balance with any available pistons.This is why 340s with forged cranks are internal balance even though the pistons are heavier than a 360s pistons,which is a external balance engine.Also most all cranks are made offshore and very similar in raw castings,its the finish work done here by the various companies that sets them apart.
 
I understand what you are saying.I'm looking for specific pieces that would fit this description.Has anybody done this before within these guidelines?Bob
 
Have you bought the crank yet? If not then buy a stroker kit and have your local shop balance it.
 
Bill.not the answer I'm looking for,but thanks anyway.Let me rephrase the question so maybe a more helpful reply will be sent.What con rod/piston assembly weights will various brands of forged 4.0" cranks support without adding internal weight or using external weights?Sorry if the question was not clear the first time.(insert smiley face here)Bob
 
The aftermarket cranks,both cast and forged,are mostly designed to be internally balnaced.The targeted bob weight for the 4" cranks seems to be around 1850 grams,that seems to be the average for cast and forged and also different brands.Therefore ,using a standard 6.123 rod and any of the forged pistons available,this bob weight is easily acheived without having to add heavy metal to the crank. An H beam rod avereages about 40 grams heavier than an I beam rod,a cast or Hyperutectic piston is heavier than a forged piston.For example : a Scat 7/16 bolt I beam rod weighs 591 grams,a Wiseco Pro-Tru forged flat top piston and pin are 566gr,spirolocks are 4 gr,rod bearings are anout45gr,a typical ring pack is about 49gr.The bob weight for this combo would be 1728gr which is well below what the crank is designed for,this means the you have to remove material from the crank counterweights to get the crank to balance.If your bob weight is more than what the crank is designed for then you have to add heavy metal to it to internally balance it or use a balancer and flywheel with a counterweight and externally balance it.
 
abdywgn said:
Bill.not the answer I'm looking for,but thanks anyway.Let me rephrase the question so maybe a more helpful reply will be sent.What con rod/piston assembly weights will various brands of forged 4.0" cranks support without adding internal weight or using external weights?Sorry if the question was not clear the first time.(insert smiley face here)Bob
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Maybe it got clouded with the extra info but in my post I said any combo of pistons and rods can be used with a forged crank and be internallly balanced.
 
I built a 408 stroker from a 5.9 L magnum engine. It has a Mopar 4" stroker crank with K1 rods and CP pistons. It was internally balanced and it did need mallory metal to achieve the balance. The piston CP # S4040 and weight is 455 gms. The K1 rod weight is 729 gms. So there is some combo of parts that do require extra weight. I don't know how the Mopar crank compares to other cranks for counterweights. Maybe the companies that sell the stroker kits can put together a set that doesn't need added weight. But I don't think that you can put parts in that will balance without doing the actual balancing operation.
 
I think the original poster knows he has to balance it. I just think he wants to avoid having to use mallory to get it internally balanced. The forged cranks are heavier then cast and they is why they can usually be balanced internally without mallory.
 
Thanks to you all who have replied.Monte,thank-you for the piece by piece description;guess I really needed to know the basics to understand the operation.I reread all the posts and they all are helpful.And,yes,I am trying to get away from adding metal.I read somewhere that the added stroke also adds into the balancing weight but not sure what that factor is.My next step would be to contact the crank sellers and ask what the bob weights are for their item.Thanks again to you all for your insight!Bob
lighter-better-faster
 
the rod weight is a big factor in determining (and getting) a light bob weight. So as long as you have light weight pistons and a decent set of rods it should not be too hard to get an internal balanced forged crank assembly.
with a 3.79 stroke, Eagle I-beam rods and Diamond forged pistons my 388ci came to 1826gms bob weight - and lots of metal removed from the crank counterweights to balance.
 
the easiest way to look at it is cast cranks that are internally balanced need Mallory. Some more than others. All forged cranks are heavy enough as they are to simply need the weight removed, so no Mallory needed.
 
abdywgn said:
Bill.not the answer I'm looking for,but thanks anyway.Let me rephrase the question so maybe a more helpful reply will be sent.What con rod/piston assembly weights will various brands of forged 4.0" cranks support without adding internal weight or using external weights?Sorry if the question was not clear the first time.(insert smiley face here)Bob
Click to expand...
Don't know bout you dismantler , but I need a simple answer. I got H rods I am looking at , a cast 3.58" crank, in a 340 block..asking, can I use flat top forged pistons without taking it to the machinist to balance. Would it be considered internally or externally balanced,?
 
Jessearent said:
Don't know bout you dismantler , but I need a simple answer. I got H rods I am looking at , a cast 3.58" crank, in a 340 block..asking, can I use flat top forged pistons without taking it to the machinist to balance. Would it be considered internally or externally balanced,?
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Any combination should be balanced.
 
Jessearent said:
Don't know bout you dismantler , but I need a simple answer. I got H rods I am looking at , a cast 3.58" crank, in a 340 block..asking, can I use flat top forged pistons without taking it to the machinist to balance. Would it be considered internally or externally balanced,?
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You don't have a grinder around to do the balance job yourself? Might come in handy to turn the mains down on your 360 crank as well.
 
Grinder and scale all you need? Don't you need some sort of machinist balancer ...you know, like they spin the tire and put weights on it in a certain place?
 
Jessearent said:
Grinder and scale all you need? Don't you need some sort of machinist balancer ...you know, like they spin the tire and put weights on it in a certain place?
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I figured someone with the skills to bore a block on a drill press would have a work around.
 
The answer is do you know the designed bobweight of the crank. Even then, it's a crapshoot that it will be good. Nobody can reasonably answer your question.

Nice revival of a 14 year old thread! :)
 
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Dicer said:
Post a report....well keep it simple, like on a scale of 1 to a 2 maybe.
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Seems kinda redundant, where's all the knowledge. H rods will all weight the same. Pistons will be the same weight and the crank we don't mess with....don't see a reason to balance .Enlighten me. Is the factory gonna sell such cramp that we need to double check?
 
Jessearent said:
Seems kinda redundant, where's all the knowledge. H rods will all weight the same. Pistons will be the same weight and the crank we don't mess with....don't see a reason to balance .Enlighten me. Is the factory gonna sell such cramp that we need to double check?
Click to expand...
Hell I thought you were the one that was going to teach all of us?
 
Gee! Anyone who builds an engine whether std or modified and doesn't rebalance it needs there head read! The factory balance jobs are questionable to say the least!
 
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